Structure for mounting vertical blind slats



May 17, 1966 A. KRULL STRUCTURE FOR MOUNTING VERTICAL BLIND SLATS 2 Sheets-Sheet l I Filed Sept. 5, 1963 R M m Q m mmfl m H 0 3 4 I Ir United States Patent 11 Claims. (a. 160-196) The present invention relates to blinds and in particular to blinds which have vertical slats.

The .slats of such blinds are usually supported for movement by an elongated support member extending along an upper part of the blind, this support member usually being hollow .and the slats respectively having top end portions which extend through a slot in the bottom wall of the hollow support member into the interior of the latter where the top end portions of the slats are connected to members which are guided for movement along the support member and for shifting in known manner as shown in US. Patent 1,351,229 and French Patent 1,034,536.

In order to adjust the amount of light entering such a blind, the vertical slats thereof are turnable about their longitudinal vertical :axes, respectively, with the result that the members connected to the top ends of the slats and supported by the support member tend to turn relative to the support member. Because of this tendency of the elements at the top ends of the slats to turn relative to the support member, these elements often bind and resist and prevent free movement of the slats along the support member.

It is accordingly a primary object of the present in vention to overcome the above drawbacks.

More particularly, it is an object of the invention to connect the top ends of the slats to shiftable members capable of being guided along the support member of the blind in such a way that free movement of the slats is at all times guaranteed and binding or undesirable resistance to such movement is'reliably prevented.

It is furthermore an object of the present invention to provide a blind of the above type in which the slats are capable of being moved very close to each other while retaining the efficient guiding of the slats, which is to say preventing binding or resistance to movement of the slats.

It is also an object of the present invention to provide a structure which is capable of releasably holding the slats in predetermined angular positions with respect to their longitudinal axes, respectively.

Also, it is an object of the present invention to provide an arrangement in which a very large number of slats can .be located very close to each other in a relatively small amount of space.

Furthermore, the objects of the present invention include shiftable members connected to the top ends of the slats and guided for movement by the support members, with the possibility of constructing all of the shiftable members identically so that they can be very inexpensively manufactured by mass production techniques.

With these objects in view the invention includes, in a blind which has vertical slats, an elongated horizontal supporting wall having a pair of elongated edge portions which define between themselves a longitudinal slot through which top end portions of vertical blind slats extend. A pair of guide means are carried by this wall at an upper side thereof and respectively extend along these edge portions which define the slot. A plurality of identical shiftable members are respectively connected to the top end portions of the slats, are located over the wall, and each have an intermediate portion in the immediate vicinity of the top end portion of the slat to which it is connected and a pair of opposed, long and 7 short end portions between which this intermediate portion is located. The long end portion of each shiftable member has, in the longitudinal direction of the slot, a dimension substantially greater than the dimension of the intermediate portion of the shiftable member in this direction, and the short end portion of each shiftable member has in the same direction a dimension which is not greater than the dimension of the intermediate portion, and the end portions of each shiftable member respectively engage the pair of guide means to be guided thereby. The shiftable members are arranged in a row along the wall with each pair of adjoining shiftable members oriented oppositely with respect to each other so that the long end portion of one shiftable member is followed by the short end portion of the next shiftable member along each guide means. In this way the intermediate portions of the shiftable member, and the top end portions of the slats therewith, can be located at a distance from each other which is substantially less than the above dimension of the long end portion of each shiftable member, while at the same time the long end portion of each shiftable member extends along the guide member which it engages through a distance sufiicient to provide etfective guiding of each shiftable member.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to itsconstruction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIG. 1 is a transverse, sectional elevation of one possible embodiment of a structure according to the present invention;

FIG. 2 is a fragmentary sectional plan View along II-II of FIG. 1 in the direction of the arrows;

FIG. 3 is a transverse sectional view of another embodiment of a structure according to the present invention;

FIG. 3a is a fragmentary sectional elevation taken along the line Illa-411a of FIG. 3 in the direction of the arrows; and

FIG. 4 is a fragmentary sectional plan view taken along the line IV-IV of FIG. 3 in the direction of the arrows. FIG. 5 is a longitudinal sectional elevation along the line VV of FIG. 4; the slats are shown in the left in closed position and in the right in extended and shifted position.

Referring to FIGS. 1 and 2, there is shown therein an elongated support member 1 in the form on an extrusion which may be made of any suitable light metal or plastic. This support member 1 is adapted to be mounted in a known way in a position extending horizontally across the top of a window which is provided with the blind of the invention. The elongated hollow extrusion 1 has a bottom wall 1a which is horizontal, and it will be seen that this elongated horizontal supporting wall 1a has a pair of inner elongated parallel edge portions which define between themselves the slot 2 through which the top end portions 4 of vertical blind slats extend. These top end portions 4 of the slats are simply in the form of cylindrical rods fixed at their bottom un illustrated ends in a known way to the top ends of the slats, respectively.

The elongated horizonal supporting wall 1a carries at an upper side thereof a pair of guide means 1b which respectively extend along the edge portions of the wall 1a which define the slot 2, and the pair of guide means are simply in the form of a pair of guide flanges 1b which are integral with the wall 1a and which respectively have upper rounded edge portions.

A plurality of identical shiftable members 3'are respectively connected to the top end portions 4 of the slats, are located over the wall 1a, and each have an intermediate portion 3a in the immediate vicinity of the top end portion 4 of the slat to which it is connected. It will be seen that each intermediate portion 3a is in fact in the form of a tube extending with considerable play through the slot 2, and the top end portion 4 of the slat extends through the tubular intermediate portion 3a, so that the intermediate portions 311 of the shiftable members 3 are in fact respectively formed with Openings through which the top end portions 4 of the slats respectively extend. These top end portions 4 have head ends 44, respectively, which respectively rest on the intermediate portions 3a of the shiftable members 3, so that in this way the slats are carried by the shiftable members 3 while at the same time being turnable relative thereto, respectively.

Each shiftable member 3 is provided with a long end portion 3b and with an opposed short end portion 3 and in accordance with the present invention the long end portion 3b of each shiftable member 3 has, in the longitudinal direction of the slot 2, a dimension a which is substantially longer that the dimension of the intermediate portion 3a in the same direction, while the short end portion 3) of each shiftable member 3 has in the longitudinal direction of the slot 2 a dimension which is not greater than this dimension of the intermediate portion 3a. In fact, in the example illustrated in FIGS. 1 and 2, the identical shiftable members 3 have their intermediate portions 3a arranged midway between the ends of their long end portions 3b, respectively, while their short end portions 3 are substantially shorter than the intermediate portions 3a and located midway between the ends of the latter, respectively.

Each long end portion 3b is formed at is underside with an elongated groove 30 which receives the guide means 1b engaged by the particular long end portion 311, and each shiftable member 3 is provided in its groove So with rounded projections 3a! which respectively slidably engage the opposed side faces of the guide means 1b. In addition, each shiftable member 3 is provided at the ends or" its groove So with a pair of downwardly directed transverse projections 3e, respectively and these projections 3e rest on and directly engage the top surface of the guide means 111. On the other hand, the short end portion 3 of each shiftable member simply has a flat bottom face resting on the guide means 1b. In this way each shiftable member 3 is provided with a threepoint support system so that the position of each shiftable member 3 is statically determined with respect to r the pair of guide flanges 1b, and thus it becomes possible with this construction to arrange the row of shiftable members so that each pair of adjoining shiftable members 3 are oriented oppositely with respect to each other, as is particularly apparent from FIG. 2. Thus, the greater length of the long end portion 3b of each shiftable member 3 enables it to cooperate with the guide means 1b which it engages to be reliably guided thereby so as to guarantee free longitudinal shifting movement of each shiftable member 3 without any possible binding thereof, and of course the short end portions 3 simply rest on and slide freely along the guide flanges. Moreover, as is also apparent from FIG. 2, it is possible to shift the members 3 and the vertical slats therewith to the position illustrated in FIG. 2 where the end faces of the shiftable members 3 engage each other over their total areas. Thus, even though relatively long end portions 3b are provided for the purpose of reliable guiding of the shiftable members, nevertheless the distance between the slats is not determined by-the length of the long end portions 31) of the shiftable members. As may be seen from FIG. 2, the distance 1) between a pair of adjoining slats is substantially less than the length a of each long end portion 312, so that with the structure of the invention it is possible to locate the slats very close to each other while providing each shiftable member with a structure longer than the shortest distance between the slats for guiding purposes. It will be seen that it is only the length of the intermediate portions 3a, in the longitudinal direction of the slot 2 which limits the extent to which the slats may be moved toward each other.

According to the embodiment shown in FIGS. 3 and 4, the shiftable members 3 have a construction substantially the same as those of FIGS. 1 and 2, the difference being primarily with respect to the length of the members 3 in the longitudinal direction of the slot 2. With the embodiment of FIGS. 3 and 4, however, upper and lower horizontal supporting walls are provided, and thus it will be seen that the elongated hollow extrusion which forms the support member 5 shown in FIG. 3 has an upper wall 1:: formed with a slot 2 in the same way as the lower wall la which is identical to the wall of FIG. 1, and these upper and lower walls of FIG. 3 are coextensive, with the upper wall It: aligned over the lower wall 1a so that the pair of slots 2 of FIGS. 3 and 4 are also in alignment with each other and of course are also coextensive. Each of the walls 1a of FIGS. 3 and 4 are provided along their edge portions which define the slots 2, respectively, with the upwardly directed, integral guide flanges 1b which form the guide means for the shiftable members 3, as described above. Theseshiftable members 3 of FIGS. 3 and 4 are provided at their long end portions with grooves which receive the guide flanges and with projections engaging these guide flanges in exactly ti e same way as described above in connection with FIGS. 1 and 2, and of course the short end portions 3] simply have flat bottom faces resting on the guide flanges 1b.

Because of the arrangement of a pair of walls 1a one over the other, it is possible to position the row of upper shiftable members 3 so that they are offset with respect to the lower shiftable members 3 and thus the plurality of rods 4 which extend to the upper row of shiftable members 3 can pass respectively between the several shiftable members 3 of the lower row, as is particularly apparent from FIG. 4. Of course, the shiftable members 3 of the upper row are identical with those of the lower row which are illustrated in FIG. 4.

As a result of this feature the intermediate portions 3a of the lower row are spaced from each other inthe position of the part shown in FIG. 4 by a distance greater than the intermediate portions 3a of the shiftable members 3 of FIG. 2, and as a result it becomes possible to provide the long end portions 3b of FIGS. 3 and 4 with a length a considerably greater than the length a shown in FIG. 2, so that an even better guiding of the shiftable members 3 is provided with the embodiment of FIGS. 3 and 4. However, it will be seen that the slats with the embodiment of FIGS. 3 and 4 need not be located from each other by a distance greater than with the embodiment of FIGS..1 and 2, when they are located as close as possible to each other as shown in FIG. 4. Thus, it will be seen that the distance b between a pair of adjoining slats, indicated in FIG. 4, is equal to the distance b shown in FIG. 2. On the other hand, the length a is still substantially greater than the distance 1) between the intermediate portions of a pair of adjoining shiftable members 3. Therefore, with the embodiment of FIGS. 3 and 4 it becomes possible to provide even longer end portions 317, as compared to the embodiment of FIG. 2, without requiring the slats to be spaced from each other by a distance greater than with the embodiment of FIG. 2. Moreover, it will be seen also that with the embodiment of FIG. 4 it is possible to provide the head ends 4a of the rods 4 with somewhat larger diameters than the head ends of rods 4 of FIGS. 1 and 2.

FIG. 3a clearly indicates how the projections 3e at the ends of each groove 30 engage the top edge of the guide flanges 1b.

It is often desirable, with slatted blinds of the above type, to be able to retain the slats in predetermined angular positions, with respect to their longitudinal axes. For example, it is desirable to be able to retain the slats in their extended position and shifted in their fully closed position with their edges overlapping each other, as shown in the right of FIG. 5, andthe structure of the invention includes a means for accomplishing this result. Thus, the head end 4a of each rod 4 and the intermediate portion 3a of each shiftable member 3 on which the head end 4a rests are provided with cooperating parts one of which is in the form of a projection and the other of which is in the form of a recess receiving this projection when the slat is in the predetermined angular position, so that in this way the slat will be retained in the particular angular position. In order to turn the slat from this position it is necessary for the entire slat to shift to a very small .extent longitudinally while the projection moves within the recess. Thus, referring to FIGS. 1-5 it will be seen that each head end 4a carries a pair of opposed projections 4b which are respectively received in a pair of opposed recesses 3g formed in the upper face of each shiftable member 3, and thus the location of the projections 4b in the recesses 3g determines a particular angular position of the slat. In order to displace the slat from this position, it is simply turned and the projections 4bride up the inclined bevelled edges of the recesses 3g. Thus, with this construction it is possible when the projections 4b are in the recesses 3g to releasably retain the slats in a predetermined position such as, for example, the closed position where the slats engage each other.

Of course, the invention is not limited to the particular examples illustrated in the drawings and described above.

Thus, for example, it is possible to use the structure of the invention also with that type of blind which includes, instead of the individual slats, a continuous curtain or sheet which has the portions which correspond to slats interconnected by fold lines so that the continuous curtain or sheet has a folded construction enabling it to be collapsed or expanded, and with such a blind the individual portions of such a sheet would also be connected to the rods 4, the only difference being that these rods 4 would necessarily turn with respect to the intermediate portions 3a of the shiftable members 3 during shifting of the latter toward and away from each other. Also, the structure of the invention can be used with that type of structure where the slats or curtain are supported only at their tops or at their tops and bottom-s. Also, instead of providing an arrangement as shown in FIG. 2 where the total end faces of the shiftable members engage each other, upon shifting of the members 3 toward each other, it is possible also to provide a construction where these end faces engage each other only at localized areas thereof.

It will be. understood that each of the elements described above, or two or more together, may also find a useful application in other types of blinds differing from the types described above.

While the invention has been illustrated and described as embodied in adjustable blinds, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a blind having vertical slats, in combination, an elongated horizontal supporting wall having a pair of elongated edge portions defining between themselves a longitudinal slot; a pair of guide means carried by said wall at an upper side thereof and respectively extending along said edge portions; and a plurality of identical unitary shiftable members each of which is connected to the top end portion of one of said slats, located over said wall, and each having an intermediate portion in the immediate vicinity of the top end portion of the slat to which it is connected and a pair of opposed, long and shortend portions being integral with said intermediate portion and located on opposite sides thereof, said long end portion having in the longitudinal direction of said slot a dimen sion substantially greater than the dimension of said intermediate portion in said direction and said short end portion having in said direction a dimension which is not greater than said dimension of said intermediate portion followed by said short end portion of the next shiftable member along each guide means whereby the central portions of adjacent slats can be located at a,distance from each other substantially less than said dimension of said long end portion of each shiftable member while said long end portion of each shiftable member at the same time extends along the guide means which it engages through a distance suflicient to provide effective guiding of each shiftable member.

2. In a blind as recited in claim 1, each shiftable member having the intermediate portion thereof arranged substantially midway between the ends of the long end portion thereof.

.3. In a blind as recited in claim 1, said shiftable members being guided by said guide means for shiftable movement toward each other to a position where they engage each other, and said shiftable members respectively having end faces, the total areas of which engage each other in said position of said shiftable members.

4. In a blind having vertical slats, in combination, an elongated horizontal supporting wall having a pair of elongated edge portions defining between themselves a longitudinal slot; a pair of guide flanges respectively connected to and extending upwardly from and along said edge portions; and a plurality of identical unitary shiftable members each of which is connected to the top end portion of one of said slats, located over said wall and guide flanges, and each having an intermediate portion in the immediate vicinity of the top end portion of the slat to which it is connected and a pair of opposed, long and short end portions being integral with said intermediate portion and located on opposite sides thereof, said long end portion having in the longitudinal direction of said slot a dimension substantially greater than the dimension of said intermediate portion in said direction and said short end portion having in said direction a dimension which is not greater than said dimension of said intermediate portion and said intermediate portion having in said direction a dimension exceeding the thickness of the slat connected thereto, said end portions of each shiftable member respectively resting on said pair of guide flanges to be guided thereby and said long end portion of each shiftable member being formed with an elongated groove which receives the respective-guide flange, said shiftable members being arranged in a row along said wall with each pair of adjoining shiftable members oriented oppositely with respect to each other so that said long end portion of one shiftable member is followed by said short end portion of the next shiftable member along each guide flange whereby the central portions of adjacent slats can be located ata distance from each other substantially shiftable member while said long end portion of each shiftable member at the same time extends along the guide flange which it engages through a distance sufficient to provide effective guiding of each shiftable member.

5. In a blind as recited in claim 4, each shiftable member having in said groove of said long end portion thereof projections which engage opposed faces of said flange.

6. In a blind as recited in claim 4, each shiftable member having at the ends of said groove of said long end portion thereof downwardly directed projections, respectively, which engage the upper edge of said flange.

7. In a blind as recited in claim 4, the short end portion of each shiftable member having a flat bottom face engaging the top edge of the guide flange on which it rests.

8. In a blind having vertical slats, in combination, an elongated horizontal supporting wall having a pair of elongated edge portions defining between themselves a Iongitudinal slot; apair of guide means carried by said wall at an upper side thereof and respectively extending along said edge portions; and a plurality of identical unitary shiftable members each of which is connected to the top end portion of one of said slats, located over said wall, and each having an intermediate portion in the immediate vicinity of the top end portion of the slat to which it is connected and a pair of opposed, long and short end por- Y tions being integral with said intermediate portion and located on opposite sides thereof, said long end portion having in the longitudinal direction of said slot a dimension substantially greater than the dimension of said intermediate portion in said direction and said short end portion having in said direction a dimension less than said dimension of said intermediate portion and said intermediate portion having in said direction a dimension exceeding the thickness of the slat connected thereto, said end portions of each shiftable member respectively engaging said pair of guide means to be guided thereby and said shiftable members being arranged in a row along said wall with each pair of adjoining shiftable members oriented oppositely with respect to each other so that said long end portion of one shiftable member is followed by said short end portion of the next shiftable member along each guide means whereby the central portions of adjacent slats can be located at a distance from each other substantially less than said dimension of said long end portion of each shiftable member while said long end portion of each shiftable member at the same time extends along the guide means which it engages through a distance sufficient to provide effective guiding of each shiftable member.

9. In a blind having vertical slats, in combination, an elongated horizontal supporting wall having a pair of elongated edge portions defining between themselves a longitudinal slot; a pair of guide flanges respectively connected to and extending upwardly from and along said edge portions, said guide flanges each having a rounded upper edge portion; and a plurality of identical shiftable members each of which is connected to the top end portions of the slats, located over said Wall and guide flanges, and each having an intermediate portion in the immediate vicinity of the top end portion of the slat to which it is connected and a pair of opposed, long and short end portions betwen which said intermediate portion is located, said long end portion having in the longitudinal direction of said slot a dimension substantially greater than the dimension of said intermediate portion in said direction and said short end portion having in said direction a dimension which is not greater than said dimension of said intermediate portion and said intermediate portion having in said direction a dimension exceeding the thickness of the slat connected thereto, said end portions of each shiftable member respectively resting on said pair of guide flanges and said long end portions of each shiftable member has at each end thereof a pair of opposite portions respectively engaging the guide flanges at which it rests on opposite side faces thereof to be guided thereby in longitudinal direction and said shiftable members being arranged in a row along said wall with each pair of adjoining shiftable members oriented oppositely with respect to each other so that said long end portion of one shiftable member is followed by said short end portion of the next shiftable member along each guide flange whereby the central portions of adjacent slats can be located at a distance from each other substantially less than said dimension of said long end portion of each shiftable member while said long end portion of each shiftable member at the same time extends along the guide flange which it engages through a distance suflicient to provide effective guiding of each shiftable member.

10. In a blind having vertical slats, in combination, an elongated horizontal supporting wall having a pair of elongated edge portions defining between themselves a longitudinal slot; a plurality of top end portions of vertical blind slats extending through said slot and each having a head end located over said slot; a pair of guide flanges respectively connected to and extending upwardly from and along said edge portions; and a plurality of identical shiftable members respectively connected to said top end portions of said slats, located over said wall, and respectively having intermediate portions formed with openings through which said top end portions of said slats respectively extend and on which said head ends respectively rest so that said slats are turnable relative to said intermediate portions of said shiftable members, respectively, each shiftable member having a pair of opposed, long and short end portions between which said intermediate portion is located, said long end portion having in the longitudinal direction of said slot a dimension substantially greater than the dimension of said intermediate portion in said direction and said short end portion having in said direction a dimension which is not greater than said dimension of said intermediate portion and said intermediate portion having in said direction a dimension exceeding the thickness of the slat connected thereto, said end portions of each shiftable member respectively engaging said pair of guide flanges to be guided thereby and said long end portion of each shiftable member being formed with an elongated groove which receives the respective guide flange, said shiftable members being arranged in a row along said wall with each pair of adjoining shiftable members oriented oppositely with respect to each other so that said long end portion of one shiftable member is followed by said short end portion of the next shiftable member along each guide flange whereby said intermediate portions of said shiftable members and said top end portions of said slats therewith can be located at a distance from each other substantially less than said dimension of said long end portion of each shiftable member while said long end portion of each shiftable member at the same time extends along the guide flange which it engages through a distance suflicient to provide effective guiding of each shiftable member, each head end and intermediate portion on which it rests respectively having a pair of cooperating parts one of which is in the form of a projection and the other of which is in the form of a recess receiving said projection only when the top end portion of the slat is in a predetermined angular position relative to the intermediate portion of the shiftable member to thus hold, when said projection is received in said recess, the respective slat in a predetermined angular position relative to said guide flanges.

11. In a blind having vertical slats, in combination, upper and lower elongated horizontal supporting walls each having a pair of elongated edge portions defining between themselves a longitudinal slot, said walls being substantially identical and coextensive, with said upper wall located in alignment with said lower wall over the latter so that said slots are also coextensive and in alignment with each other; a plurality of top end portions of vertical blind slats some of which extend only through the slot of the lower wall and others of which extend through the slots of both walls; a pair of guide means carried by each wall at an upper side thereof and respectively extending along said edge portions of each wall; and a plurality of identical shiftable members respectively connected to the top end portions of the slats, located over each wall, and each having an intermediate portion in the immediate vicinity of the top end portion of the slat to which it is connected and a pair of opposed, long and short end portions between which said intermediate portion is located, said long end portion having in the longitudinal direction of each slot a dimension substantially greater than the dimension of said intermediate portion in said direction and said short end portion having in said direction a dimension which is not greater than said dimension of said intermediate portion and said intermediate portion having in said direction a dimension exceeding the thickness of the slat connected thereto, said end portions of the plurality of shiftable members over said upper wall respectively engaging said pair of guide means of said upper wall to be guided thereby, and said shiftable members being arranged along said walls in a pair of rows with each pair of adjoining shiftable members oriented oppositely with respect to each other so that the long end portion of one shiftable member is followed by the short end portion of the next shiftable member along each guide means, and the shiftable members which are located over said upper wall being respectively offset with respect to the shiftable members extending over said lower wall and the top end portions of the slats connected to the upper row of shiftable members extending through the lower slot respectively between the intermediate portions of the lower row of shiftable members, whereby said intermediate portions of said shiftable members and said 1 top end portions of said slats therewith can be located at a distance from each other substantially less than said dimension of said long end portion of each shiftable member while said long end portion of each shiftable member at the same time extends along the guide means which it engages through a distance sutficient to provide effective guiding of each shift-able member.

References Cited by the Examiner References Cited by the Applicant UNITED STATES PATENTS 1,043,492 11/ 1912 Werner et a1.

HARRISON R. MOSELEY, Primary Examiner.

CHARLES E. OCONNELL, Examiner.

D. L. TAYLOR, Assistant Examiner. 

1. IN A BLIND HAVING VERTICAL SLATS, IN COMBINATION, AN ELONGATED HORIZONTAL SUPPORTING WALL HAVING A PAIR OF ELONGATED EDGE PORTIONS DEFINING BETWEEN THEMSELVES A LONGITUDINAL SLOT; A PAIR OF GUIDE MEANS CARRIED BY SAID WALL AT AN UPPER SIDE THEREOF AND RESPECTIVELY EXTENDING ALONG SAID EDGE PORTIONS; AND A PLURALITY OF IDENTICAL UNITARY SHIFTABLE MEMBERS EACH OF WHICH IS CONNECTED TO THE TOP END PORTION OF ONE OF SAID SLATS, LOCATED OVER SAID WALL, AND EACH HAVING AN INTERMEDIATE PORTION IN THE IMMEDIATE VICINITY OF THE TOP END PORTION OF THE SLAT TO WHICH IT IS CONNECTED AND A PAIR OF OPPOSED, LONG AND SHORT END PORTIONS BEING INTEGRAL WITH SAID INTERMEDIATE PORTION AND LOCATED ON OPPOSITE SIDES THEREOF, SAID LONG END PORTION HAVING IN THE LONGITUDINAL DIRECTION OF SAID SLOT A DIMENSION SUBSTANTIALLY GREATER THAN THE DIMENSION OF SAID INTERMEDIATE PORTION IN SAID DIRECTION AND SAID SHORT END PORTION HAVING IN SAID DIRECTION A DIMENSION WHICH IS NOT GREATER THAN SAID DIMENSION OF SAID INTTERMEDIATE PORTION AND SAID INTERMEDIATE PORTION HAVING IN SAID DIRECTION A DIMENSION EXCEEDING THE THICKNESS OF THE SLAT CONNECTED 